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    <title>Document</title>
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    <script>
        function fun(fn) {
            fn();
        }
        fun(() => {
            console.log(111);
        })
        
        function fn1() {
            console.log(222);
        }
        fun(fn1)

        function ADD() {
            this.state = 'Pending';
        }
        ADD.prototype.then = function() {
            let a = new ADD();
            return a.state;
        }
        console.log(new ADD().then()+ '-----');
    </script>
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